Field Notes: The Nose Rules

The nose dominates the face and has more importance than either eyes or ears in a dog's interpretation of his world. The more droplets of moisture on a dog's nose, seen here, the better smeller he can be. The best noses can drip like a runny nose on a child. Dogs interpret primarily with their nose. They see shapes and can react with fear or anxiety until they are able to smell the shape.

The nostrils are moist and mobile. The folds on each side, shown here, allow them to move and expel air. They quiver and rotate in order to seek out the direction of a scent. The moisture aids the nose in detecting scent. If scent is airborne, the dog raises her nostrils to the breeze, if it is buried in the ground, those nostrils can often come up with a nose-full of dirt.

The other day I watched my canine companion, Zina, put her nose to the breeze and then bury it deep in the grass near the pasture fence. Her excitement reminded me of the days when my German Shepherds were able to roam freely in the fields before the housing development set in. Their nose-down, tail up odyssey fulfilled every scent-driven need in their bodies.

Dogs are news junkies and scent is their “Washington Post.” They interpret their world with a sniff as readily as we do with our sight. Dogs can discern sex, age, health, and more from another dog’s simple stop at a tree, as well as learn what this canine had for dinner- proteins and amino acids are the clue.

Each year brings new skills to the trained dog’s nose. They can discern cancerous lesions before they appear; detect diabetes and sniff out invasive plants in impossible places.

Sniffing is a dog’s most stimulating experience, so what happens in that joyous moment when a scent goes from nose to neuron? Your pet’s nose is made up of a very complicated sensing system that enables her to decipher each smell and register it.

ONCE A SCENT is registered in the memory, it is there for life. By the age of three months, 80 percent of a puppy’s experience is indelibly imprinted on its brain, scent being one of them. Thus, a traumatic event involving a particular smell early on could be adversely relived when exposed to it many years later.

The dog's nose is made of three layers of cells, the outer called the stratum corneum (horny layer). The grooves or textured appearance on the surface is unique to every animal, like fingerprints on humans. Nose prints are being used today to identify dogs. You can take a nose print of your dog by drying it first then coating the nose with food color, (not ink, please), and pressing it (sides also) with soft paper.

The part of a dog’s brain used for analyzing smell is about 40 times larger than that of a human and 10,000 times more sensitive. That dog lying on our bed with us has over 22 square feet of nasal membrane packed in her moist, quivering nose, compared to 3 square feet in ours. The dog’s olfactory lobe, which decodes scent messages, dwarfs that of a person’s.

“If humans are able to detect one drop of a specific substance diluted in a few drops of water, dogs would be able to detect one drop in 25 million barrels,” said Dr. Bonnie Beaver of Texas A&M University College of Veterinary Medicine.

Imagine the deliciousness of the vast array of scents that waft across a whopping 225 million scent receptors in your German Shepherd’s nose and act as a lightning rod for odors. Compare that to the human schnoz, which must make do with a minuscule five million receptors.

And, not all noses are created equal. The Dachshund has 125 million scent-detecting cells and the Fox Terrier 147 million. They were bred for hunting and digging while the Bloodhound has 300 million — so there is not much that can elude that sniff.

Wildlife biologist Alice Whitelaw, director of Programs at Working Dogs for Conservation in Three Forks, Montana, works with scenting dogs but still finds their skills a mystery. You can ask 1 in 10 people about how a dog actually processes scent and their answers can all be different, she said. We still don’t fully understand the dog’s scenting abilities. Her conservation program’s dogs are trained to detect everything from a Gila monster to invasive snails to carnivore scat (feces).

SCENT RETRIEVAL begins with sniffing, the kind we hear when our pet buries her nose in a bush. Sniffing is a disruption of the dog’s regular breathing pattern and consists of rapid inhalations and exhalations, which come in sets of three to seven sniffs each. Sniffing allows air to stay in the nasal chambers and is believed to be initiated by a bony structure not present in humans called a “subethmoidal shelf,” which is found below the bones of the dog’s nasal cavity.

As the particles of sniffed air enter the dog’s nostrils they pass onto the lining of the nasal membranes, the olfactory epithelium, and travel to a pocket above this “shelf” where the scent molecules are trapped to prevent them from being expired when the dog breathes out.

There they accumulate with each “sniff” and interact with the olfactory receptors which are transmitted by the nerves to the brain. It is this process that allows a dog to recognize and remember scents. At about the same time, the dog’s normal breathing continues through the nose and on down to the lungs.

Then, there is the “vomeronasal organ” an auxiliary olfactory sense organ located under the nasal bones close to the nose and used to detect pheromones. It is important in the role of reproduction and social behavior. These fluid-filled sacs are located right above the roof of the mouth and open into either the mouth or nose. The vomeronasal organ is also responsible for a dog’s reflex called the Flehmen response (in German meaning “to curl the upper lip”) That curl helps move the scent into the upper part of the mouth.

In male dogs Flehmen shows up as a kind of tooth chattering in response to a specific scent or pheromone. Some males that have had no experience with females in estrus (heat) will not react to female pheromones. These dogs have to be exposed and learn from the experience.

In their groundbreaking experiments, which are still relevant and written about, the team of scientists John Paul Scott and John L. Fuller put the dogs to a test at their Bar Harbour, Maine, facility in the early 1960s. Their book, “Genetics and the Social Behavior of the Dog, is still a turn-to book on dog behavior.

In their book they wrote about placing a mouse in a one-acre field and turned a group of beagles loose to find it. It took less than a minute. A group of fox terriers took a quarter of an hour, and the Scottish terriers never did find it, with one actually stepping on the mouse.

Then there’s Seamus, a rescue Border Collie trained at Working Dogs for Conservation, who doesn’t have to sniff out mice in his line of work. His specialty: leaves, according to Whitelaw, the program director. Seamus’ target is called Dyer’s Woad, an invasive plant in Missoula, Montana. When the county loses the battle with the plant, they ask for Seamus. He shows up and not only finds the tiny plants hiding on the Missoula plain, but sniffs out the roots after the weeds have been pulled.

That’s some big league nose, a Tom Brady kind of sniffer. But, according to Whitelaw, the super sniffers at Working Dogs for Conservation need more than a nose — they need attitude. “There are some great dogs that you wouldn’t expect to do this work, but they have the drive,” she said. The program usually finds one dog in a thousand that will have the qualities to do the job.

So the next time your beloved pet takes her time sniffing every leaf, wrapping the leash around tree trunks, nose working like a hand-held vacuum, think twice before you drag her away. There’s a lot she’s missing by not sniffing.